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A 23-year-old man with diabetes mellitus has a glomerular filtration rate (GFR) significantly greater that normal,especially when he consumes excessive amounts of sweets. A decrease in which of the following parameters would tend to increase the glomerular capillary hydrostatic pressure?
A. Afferent arteriolar resistance
B. Bowman's capsular hydrostatic pressure
C. Capillary filtration coefficient
D. Efferent arteriolar resistance
E. Plasma colloid osmotic pressure
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The correct answer is A. A decrease in the resistance of the afferent arteriole (i.e., arteriolar dilation) directly
increases glomerular capillary hydrostatic pressure by lessening the drop in blood pressure that normally
occurs along the vasculature proximal to the glomerulus. [Recall that the afferent arteriole is upstream from the
glomerulus; the efferent arteriole is downstream from the glomerulus.] The glomerular capillary hydrostatic
pressure is the determinant of glomerular filtration rate most subject to physiological control.
Bowman's capsular hydrostatic pressure (choice B), capillary filtration coefficient (choice C), and plasma colloid
osmotic pressure (choice E) are important determinants of GFR but they do not have any direct effect to
increase or decrease the glomerular capillary hydrostatic pressure.
A decrease in efferent arteriolar resistance (choice D) would tend to decrease the glomerular capillary
hydrostatic pressure because the efferent arteriole is downstream from the glomerular capillaries.
